The organic electroluminescence (organic EL) display device is a thin display device of self-emission type, and has an advantage in view of display performance, for example, high visibility or small viewing angle dependency, in comparison with a liquid crystal display device. Also, in addition to an advantage in that the display can be made lighter and thinner, it has a possibility of achieving a display device having a shape, which has not been realized, by using a flexible substrate.
The organic EL display device has the excellent features as described above. However, since layers having different refractive indexes are stacked using a transparent conductive material having a high refractive index, for example, ITO, as an electrode and a metal material having a high reflectance are used, external light is reflected at the interfaces thereof, thereby causing a problem of reduction of contrast or background reflections due to internal reflection.
A typical constitution of the organic EL element is shown in FIG. 1. As shown in FIG. 1, the organic EL display device basically has a constitution in which on a TFT substrate 1, a back electrode 2, an organic layer 3 made from two or three layers including a light emitting layer, a transparent electrode or translucent electrode 4 and a transparent substrate 5 are stacked, and a positive hole injected from the back electrode 2 and an electron injected from the transparent electrode 4 are recombined in the organic layer 3 to excite a fluorescent substance or the like, thereby emitting light. The light emitted from the organic layer 3 is emitted through the transparent substrate 5 directly or after being reflected with the back electrode 2 formed from aluminum or the like. Also, in order to realize color display, for instance, a construction wherein the organic layer 3 has a structure in which pixels of three colors in total, red, green and blue, or pixels of four colors in total including white in addition to three colors are arranged in a matrix form, and a structure in which the organic layer 3 is made from an element emitting white light and is combined with a color filter to achieve a color display are proposed (for example, Patent Documents 1 and 2).
As described above, since the organic EL element has a structure in that plural layers having different refractive indexes are stacked or in that a metal electrode is used, external light is reflected at the interfaces of the respective layers to cause the problem of reduction of contrast or background reflections.
In order to inhibit the harmful influence due to the external light reflection as described above, a proposal of using an absorption type linear polarizing plate and a circular polarizing plate made from a λ/4 plate (for example, Patent Documents 3, 4, 5 and 6) and a proposal of using an absorption type linear polarizing plate, a λ/2 plate and a circular polarizing plate made from a λ/4 plate (for example, Patent Document 7) have been made.
Further, the circular polarizing plate has a large number of uses not only in the organic EL display device but also in a reflection type LCD, a semi-transmission type LCD, a transparent display, a brightness enhancement film, a pick-up for optical disc, a PS conversion element and the like.